1. Field of the Invention
This invention relates to a method of and an apparatus for controlling an electromagnetic parts feeder which feeds various types of parts by vibration of a bowl caused by an alternating magnetic field generated by an electromagnet.
2. Description of the Prior Art
A typical example of the conventional electromagnetic parts feeders comprises, as shown in FIG. 1, a bowl 2 adapted to accommodate therein a large number of parts for supply and discharge the parts while exerting vibration to the bowl, a vibrating unit 4 provided with an electromagnet or piezoelectric element for driving the bowl 2 at a predetermined resonance frequency, and a driving control system 5 for driving the vibrating unit 4. This parts feeder is adapted to electrically detect a vibration amplitude of the bowl 2 by an amplitude sensors 6 such as, for example, a photoelectric transducer and a piezoelectric element, feed it back to the driving control system 5, and control the electric current or voltage for driving the bowl 2 to drive the bowl at a constant amplitude at any time.
Since this method requires the amplitude sensor 6 to detect the vibration of the bowl 2, the construction of the system becomes complicated, the number of components for detecting the vibration increases, and also the cost becomes high.
An object of the present invention is, therefore, to provide a method of and an apparatus for controlling an electromagnetic parts feeder with simple construction and enabling accurate vibration.
In accordance with one aspect of the present invention, there is provided a method of controlling an electromagnetic parts feeder which comprises a vibrating unit provided with an electromagnet of which magnetic field vibrates at a predetermined frequency, a bowl adapted to discharge parts accommodated therein by means of the vibrating unit, a driving circuit for driving the electromagnet, and a control unit for outputting a driving signal to the driving circuit to cause a predetermined driving. The method comprises idling the driving of the electromagnet temporarily at every predetermined driving cycles of the electromagnet and controlling vibration of the electromagnet based on a signal such as a voltage or electric current obtained from the electromagnet mentioned above by its electromagnetic induction during the idling period, for instance, based on a phase difference between a waveform of this signal and the driving signal of the driving circuit mentioned above.
In a preferred embodiment, a resonance frequency of the electromagnetic parts feeder is previously measured before it is controlled. When the measurement of the resonance frequency is made, the electromagnet is driven by the driving circuit mentioned above, the driving by the driving circuit is temporarily idled at every predetermined driving cycles, and the electromotive force obtained from the electromagnet by its electromagnetic induction is measured during the idling period. The frequency at which the signal becomes maximum is assumed as a resonance frequency. Then, the electromagnet is driven by the driving circuit at the obtained resonance frequency, and the driving by the driving circuit is temporarily idled at every predetermined driving cycles. During the idling period, a signal obtained from the electromagnet by its electromagnetic induction, a phase difference between a waveform of this signal and the driving signal of the driving circuit mentioned above, and the resonance frequency mentioned above are stored in a storage element. When the vibrating unit is driven, it is driven at the resonance frequency stored. Furthermore, the control of the electromagnet is carried out in such a way that the phase difference between the waveform of the signal obtained by the electromagnetic induction and the driving signal of the driving circuit becomes equal to the stored phase difference mentioned above.
In accordance with a second aspect of the present invention, there is provided a system for controlling an electromagnetic parts feeder. This system comprises a vibrating unit provided with an electromagnet that vibrates at a predetermined frequency, a bowl adapted to discharge parts accommodated therein by means of the vibrating unit, a driving circuit for driving the electromagnet, a control unit for outputting a driving signal to the driving circuit to cause a predetermined driving and temporarily idling the driving of the electromagnet at every predetermined driving cycles of the electromagnet, a signal detecting means for detecting a waveform of a signal obtained from the electromagnet by its electromagnetic induction during the idling period, a phase difference detecting means disposed in the control unit for detecting a phase difference between the waveform of the signal obtained by the signal detecting means and the driving signal waveform of the driving circuit, and a vibration controlling means for controlling vibration of the electromagnet based on the phase difference obtained by the phase difference detecting means.
In this specification, the signal mentioned above indicates a voltage or an electric current. When the signal indicates a voltage, the terms including the word xe2x80x9csignalxe2x80x9d such as, for example, a signal waveform, a driving signal, a signal detecting means, and a driving signal waveform refer to a voltage waveform, a driving voltage, a voltage detecting means, and a driving voltage waveform, respectively. When the signal is an electric current, they refer to, for example, a current waveform, a driving current, a current detecting means, and a driving current waveform.
The method of and the apparatus for controlling the electromagnetic parts feeder as constructed above are capable of accurately detecting the vibration by utilizing a coil of the electromagnet as a sensor, without using a special amplitude sensor that detects the amplitude of the vibrating unit, so that the construction thereof can be remarkably simplified. Moreover, since the resonance frequency of the parts feeder is once measured and stored and the parts feeder is operated based on the stored resonance frequency and other signals or the data of phase difference, it is possible to drive the parts feeders on their respective optimal driving conditions. Since the resonance frequency can be measured again even when the construction of the parts feeder is changed, it is possible to drive the parts feeder always at suitable conditions.